The present invention relates to an air breather structure for oil seals in an automatic transmission including an automatic transmission device adjacent to a case for a final reduction device, and more particularly to a breather structure for an automatic transmission device in a four-wheel drive vehicle.
Such an automatic transmission device is lubricated with an automatic transmission fluid (ATF) and the final reduction device including a differential is lubricated with a differential oil different from the ATF in quality. In such an automatic transmission, both devices are separated by a gasket and an oil seal is provided around a rotating shaft extending across the gasket in order to prevent the mixing of both oils. In an automatic transmission device for a four-wheel drive automobile, two rotating shafts extend across the gasket. One of the rotating shafts is a hub of a reduction drive gear and the other is a drive pinion shaft in the final reduction device which extends in the opposite direction for transmitting the power of the engine to a different pair of wheels than the wheels driven through the final reduction device. Therefore, two oil seals are provided around both rotating members. Each oil seal is provided with a pair of sealing members at a space and the space is communicated with the atmosphere through an air breather passage for ensuring the sealing effect. In an air breather structure employing a pipe system, there are difficulties namely a space for the pipe system must be provided in the transmission and trouble occurs such as leakage from connections of pipes, immersion of water into the pipe, and breakage of the pipe. It has been proposed to provide the air breather passage in the junction of the final reduction case and the automatic transmission case. However, since a plurality of oil passages are formed in the junction of the automatic transmission device, it is difficult to provide an air breather passage in the junction.